Black tank vent options?

[jimmydean]

I just installed my black tank and I haven't done water supply yet, so we haven't really used it yet. But all the venting seems to be roof mount, but Scamp trailers use a side vent. I found a plastic fuel tank side vent and am considering installing it in the side of the tank. 

Since this is my first time and it's from scratch, I was interested in what others have done for venting, especially in a step van.

 

[bullfrog]

If I understand you question correctly you are wanting to vent a black tank somewhere other than the roof? The reason this is done is to disperse the smell of the fumes. Many with roof top vents use fans to disperse the fumes even more. A side vent will work but you may not be happy that it does!

 

[jimmydean]

That's my concern, but running it through the floor, then through the roof means cutting 2 more holes in my truck. If I am going to go that route, a fan would also be used.

The idea being a fuel vent valve would allow for air flow, but mitigate smell. I could be wrong (wouldn't be the first time).

 

[MrNoodly]

I think the idea behind venting through the roof is to get it above nose level. I think that's what Bullfrog meant when he wrote that you might not be happy with a side vent.

 

[bullfrog]

Exactly! A lot depends on how much and what you put in it. A separating toilet is a great idea but even it sometimes needs a vent/fan. Porta potties also build up gases as well if not vented so be sure to burp it if you don't vent it. If you are going to make an RV out of a van and use a black tank and put liquids/solids and paper products in it for 2 weeks at a time then most likely you need to consider where all the off gassing will go just like the RV manufacturers by putting a vent/fan/hole in the roof and weather protection for that vent. As a 10 gallon black tank is sometimes a requirement for long term stays I would use at least one that size and vent it through the roof as far as possible from any other vents. I personally use a separating toilet part of the year and a regular RV with black tank the rest and put toilet paper in a separate container in both cases. By using cedar chips in the separating toilet I am able to use it unvented most of the time but it does get dumped at least once a week. You do have options but there are limits and a lot depends on what you put in the tank as to how much it will off gas.

 

[jimmydean]

Maybe I don't need a vent? It's an 18.5 gallon tank because it was cheaper and it fits. I will only have 25 gallons fresh, so most our trips will likely be 3-4 days tops. Or maybe the fuel tank vent will work well enough should a vent be needed.

Thanks for the feedback, it helps.

 

[maki2]

Here is how the vent works. The vent tube inside the tank has to be up above the level of the liquid. It won't vent the gases out or allow liquids to go into the tank if that vent tube is inside of the liquid. When you add liquid that liquid is displacing the air in the tank so that air has to be able to go out a vent tube in order for the liquid to enter. You want the vent tube to go to an outlet that is higher than the tank so that the liquid does not slosh up into the tube and out of the vent.

Vents on the side of the vehicle do work to s but they do need to be constructed so when there is wind blowing across the opening or wind blowing directly into the side of the vehicle it does not push air back into the vent opening. Without the wind protection the odors from the tank can get blown back into your RV and also it induces extra pressure inside of the tank sometimes leading to odors from the tank coming into your RV.

The vent tube that extends up through the roof needs to be an inch and a half higher than the top of the roof. Then you should also have some type of vent cap cover that is suspended over the top of the tube but not touching the top of the tube. This is also to prevent the wind from blowing back down into the tube and blocking the gases in the tank from escaping. It is about air pressure, you want that air from the tank to be able to escape up and out of the tube.

Even if you are using a portable toilet you don't want to overfill it or you will block the vent that is built into the toilet and that will prevent it from being able to release the air inside the tank both to remove gases but also to allow more liquid to enter into the tank.

A tank under the sink needs a vent. Even a fresh water tank needs to have a vent in order to be able to get water into it and to prevent the sides of it from collapsing when you pump water out of it.

Vents are simply critical in plumbing, things don't work properly without them as there has to be a way to keep the pressure equalized. Although of course there are some tanks you want to build up pressure inside of such as a garden sprayer in which case the excess air pressure you add to the tank is forcing the liquid out until the pressure is equalized at which point you have to pump in more air to get the water to spray out.

 

[bonvanroulez]

Boats typically have holding tanks vented through the hull, above waterline, below nose level. They use charcoal canister filters in the vent line to mitigate odors. You can google “boat holding tank filter”, they’re not crazy expensive but they’re also pretty easy to make using pvc pipe and fittings, and activated charcoal.

Boats have the vent low because they don’t usually have a “roof” as any upper areas and surfaces are generally used as deck/living space.

 

[jimmydean]

I totally understand HOW a vent works. I am trying to avoid cutting another hole in my roof. This is why I am considering the fuel tank vent, to allow air but not waste water to flow out.

But I also don't anticipate my tank ever being more than half full.

 

[bonvanroulez]

But I also don't anticipate my tank ever being more than half full.

A partially full black tank needs venting the most. Liquid contents of the tank aren't the problem. The gases inside the tank can expand dramatically with hotter outside temperatures creating great pressure that, without a vent, will be released when you open the toilet flush valve. If that is when flushing after using the toilet the results can be nasty.

 

[maki2]

I have a small, 5 gallon max, meaning 4 gallons functional capacity grey water tank. I vent it through the side wall of my travel trailer. I also use the same vent through the sidewall on the other side for venting my marine toilet, I use a macerator pump to empty it so my portable marine toilet has a special fitting that goes into the toilet with a small vent tube on it.  There are no windows near those vents so the odor is not an issue. Plus I also use an enzyme product that helps control odors in the tanks. Just be careful where you place the vent. Putting a roof top vent in would not work well for me as I have a pop-up roof section that has zippered windows in it. The odor would blow right into those big screened opening if my waste tank vent was on the roof.

This is what I used. https://www.fisheriessupply.com/sea-dog-line-nylon-tank-vents

 

[jimmydean]

I was thinking my tank is on the driver's side and I don't have a door on that side, so we aren't over there ever.

I might start with the fuel vent, it was $7. If I need to go through the roof, I can in the corner behind the toilet.

Thanks everyone for the feedback.

 

[66788]

I installed a 1 1/2 inch ABS vent from the tank through the floor of my Grumman Olson, inside the one piece 32 inch shower wall, and out the roof. Totally invisible inside the vehicle but works great.

Remember, a good vent is essential for emptying the holding tank as well as filling and venting.